The Russian government is set to gain majority control of gas giant Gazprom after agreeing to buy an extra 10.7% stake for 203.5bn roubles ($7bn; £4bn).
The Kremlin had initially planned to merge Gazprom with Rosneft
The Kremlin plans to raise the money by floating a minority share in state-owned oil firm Rosneft.
It hopes to secure its majority stake in Gazprom by 24 June.
The deal should mean the government is moving closer to allowing the remaining shares in Gazprom to be traded freely. Foreigners currently cannot buy them.
The $7bn Moscow paid for the 10.7% stake in Gazprom is less than expected.
Investment banks Morgan Stanley and Dresdner Kleinwort had valued the stake at $8.4bn and $11.5bn respectively.
The Russian government had previously planned to merge Gazprom with Rosneft, but this idea was scrapped.
Analysts said managers at both firms had strongly resisted the merger, forcing a major government rethink.
The merger ran into difficulties after Rosneft controversially acquired Yuganskneftegas, the oil production unit of former leading oil producer Yukos.